In the drilling of oil or gas wells apparatus is employed to prevent such wells from blowing out of control during the drilling operations. Such apparatus conventionally comprises a plurality of devices known in the art as blow out preventers which are attached to the well head.
It is further conventional to provide at least two such preventers of the ram type, a typical example of one being manufactured by Cameron Iron Works and depicted on page 1435 of the Composite Catalog 1980-1981 published by World Oil. Such preventers typically include a pressure vessel housing enclosing hydraulically or mechanically actuated opposing pistons which are attached to corresponding ram blocks for puroses of urging the ram blocks in radial directions into and out of the wellbore. The ram blocks, in turn, carry faces of varying design, each having a semicircularly shaped sealing surface formed of a resilient packing material whereby when the faces are forced radially inwards by the pistons sufficiently, a cylindrical sealing surface of this resilient material is thereby formed for sealing engagement about pipe traversing the preventer bore and borehole. The closing of these ram blocks about the pipe thereby effectively seals off the preventer bore transversely about the pipe, thereby preventing undesirable escape of pressurized fluid from the wellbore.
During the drilling of hydrocarbon wells, it is necessary at various times to suspend pipe of varying outside diameters through these blow out preventers into the wellbore for purposes well known in the art. Accordingly, it is concomitantly necessary to change out the ram blocks in the preventers to accommodate these differing pipe diameters, inasmuch as for a given pair of ram blocks installed within a preventer, the radius of curvature of the sealing faces thereof define a single bore diameter adapted for sealing engagement only with pipe of a correlative outer diameter. Moreover, in order to accommodate the wide range of pipe diameters and provide correlative ram openings encountered in the art, which may typically range from 23/8 to 95/8 inches o.d., it has been conventional to disassemble the preventers and install different ram blocks with faces having sealing surfaces of a different radius of curvature to accomodate the o.d. of the particular pipe traversing the wellbore.
Unfortunately, the aforementioned blow out preventers are frequently disposed in inaccessible or hazardous locations as, for example, below the drilling rig floor, or, in the case of offshore wells, adjacent to the sea bed. It may thus be readily appreciated that such changing out of ram blocks to accomodate pipe of differing diameters is not only time consuming but frequently a dangerous and expensive operation. For example, in the case of the aforesaid preventers located on the ocean floor, as for example with a floating drilling rig, the change-out operation necessitates detaching the preventers and riser from the wellhead, lifting the preventers, which are frequently quite bulky and heavy, and their attached riser to the drilling rig, disassembling the preventers to remove the ram blocks, installing different blocks and reassembling and pressure testing the preventers, and thence returning the preventers and riser to the sea bed wellhead and reattaching them. Such operations are thus as stated extremely difficult, dangerous, time consuming and expensive, with several days of unproductive rig drilling down time being required to effect such changes.
For the foregoing reasons, methods and apparatus were long sought for effecting the modification of such preventers from remote locations to accomodate pipe of varying diameters. Thus, it has become known in the art as shown in U.S. Pat. Nos. 4,133,342 and 4,003,430 to provide various drill pipe conveyed mechanisms which were lowered proximally to the ram faces for cutting out and flushing away the resilient packing material carried by the ram blocks. Additional apparatus as shown in U.S. Pat. Nos. 3,737,974 and 3,821,838 has further been provided, also conveyed by the drill string, for transferring replacement seals from a remote location to the preventer and thence installing and securing such seals in the recess resulting from the previous operation of removing the pliable packer material in the rams.
While such technology has met with some success in certain applications, several problems were nevertheless still associated with attempts to effect the modification of ram shoe bores from a situs remotely of the preventer. For example, in the aforementioned approach, it will be recalled that one step comprised the cutting out and thus destruction of the prior packing material which was thus obviously not retrieved intact at the remote location. Moreover, such a cutting operation required that mechanisms be provided for insuring that material thus cut away was sufficiently removed from the recess in order to permit installation of the new packer material. Still further, provision was further required for insuring that such spent material was flushed from the preventer itself.
However, an even more serious problem with the prior technology related to the limitations in bore diameter of the resultant replacement seals which might thus be installed. More particularly, in such technology, it will be recalled that primarily it was the sealing material that was cut away from ram blocks which carried metalic pipe faces of a fixed radius of curvature and which could thus not be remotely varied during the seal member changing operation. Such pipe faces defined a portion of the cylindrical surface of the preventer rams adapted to circumscribe pipe of a diameter correlative to the radius of curvature of the pipe faces.
Accordingly, the portion of the replacement seals intended to sealing engage the outer periphery of the pipe could have a radius of curvature substantially equal to that of the pipe faces of the ram shoes in order to accomodate pipe of the same diameter sealed by the prior seal. Alternatively, the replacement seal could even have a portion intended to sealingly engage pipe having an even smaller radius of curvature to accomodate pipe of a correlative smaller o.d. than that previously sealed about by the preventer.
However, inasmuch as the radius of curvature of the metallic faces of the ram blocks could not be enlargened from a remote location, this effectively limited the ability to modify the preventer from a remote location so as to accomodate pipe having an o.d.TM.greater than that corresponding to this radius of curvature of the pipe faces. In other words, means were provided for remotely modifying a preventer so as to accomodate pipe o.d.'s equal to or smaller than those corresponding to the radius of curvature of the ram faces, but the pipe face o.d. of the rams first installed in the preventer when first deployed effectively limited the maximum pipe o.d. which might be accomodated and sealingly engaged by the preventer.
Still further problems were associated with prior attempts to remotely modify preventers to accomodate widely ranging pipe o.d.'s in order to sealingly engage therewith. In the removal of prior sealing material and replacement of a seal having a differing radius of curvature from a remote location, it is necessary to establish with some precision both the radial and axial position of the preventer relative to the tool performing these functions. More reliable means were sought for establishing this spatial interrelationship between the running tool relative to the preventer components. Moreover, means were also sought for more reliably and precisely establishing such radial and axial positioning of ram shoes relative to the conveying running tool both when such shoes are withdrawn from the preventer by the tool and installed within the preventer by the running tool.
Still further, a conventional replacement ram shoe adapted to replace another such shoe transported and under control from a remote location to the preventer was typically releasably attached to the ram by means of a plurality of pins and apertures in the seal and ram. When such apertures were brought in registry, they could be matingly received by such pins to releasably and retainedly interconnect the seal and the ram. Particularly in the application of the instant invention wherein it is desirable to control from a location remotely of the preventer both the removal of the prior seal as well as replacement by a new seal, the provision of such a plurality of fastening pins provided great difficulty both in effecting release of the seal from the ram block for removal as well as in reliably effecting a subsequent interconnection between the replacement seal and the ram block with the necessary integrity under the adverse conditions of the borehole environment.
Accordingly, technology was also sought in the art for providing a releasable interconnection between a ram shoe and ram block which was simpler in design and operation, reliable, and effective in controlling both such release and interconnection from a remote location.
The present invention overcomes the hereinbefore described problems as well as others, providing a novel system for effecting replacement of ram shoes in a preventer from a remote location.